1. Field of the Invention
This invention pertains to a player for a double-sided multi-layer optical disc. The player is provided with two heads, each mounted on a respective side of an optical disc. The player can read data from either side, either sequentially or simultaneously.
2. Description of the Prior Art
A double-sided multiple-layer optical disc, such as a DVD, has a very large digital data storage capacity. For example, a DVD-18 having two data layers on each side can be used to store about 18 GB of data. Therefore, double-sided DVDs are becoming the favorite medium for recording and distributing multimedia programming, such as movies. A double-sided optical disc can store the visual portion of the programming, the audio portion in one or more languages, and various additional information that may be related to the programming.
Typically, DVDs are read by players that are capable of reading only one side at a time. A DVD is first inserted into the player with its first side oriented toward the read head. The player detects that the DVD is present and directs its read head to read data from one of the layers (typically, the outer layer) while the DVD is rotated in a preselected direction. When the player is finished reading data from the first side (one or both layers), the user removes the DVD, flips it upside down and reinserts it with the second side facing the read head. The player then directs its head to read the data from one or both layers of the second side.
One major problem with this whole process is that data cannot be read from both sides of the DVD seamlessly since the DVD must be physically removed from the player and flipped around. A further disadvantage is that data cannot be read from the two sides simultaneously.
An optical disc known as the Laserdisc (LD) has also been used for distributing and playing multimedia presentations. However, a Laserdisc has several disadvantages as a result of which no LDs are made in the United States, and it is expected that very soon LDs will be phased out throughout the rest of the world as well. First, an LD is fairly large, having a diameter of about 12 in, i.e., in the same range as an LP record. Second, the LD has only a single data layer on each side, and therefore its capacity of storing information is small. Third, just like on existing DVDs, data on the two sides of an LD are disposed along respective spirals, with the spiral on one side being identical to the spiral on the other. As a result, once an LD has been inserted into a standard player to play one of its sides, it must be removed and flipped over before the second side can be played.
Players are known that were provided with two lasers on their heads to enable the players to play different types of media including LDs, CDs, DVDs, etc. The players also include mechanisms that switch the heads from one side of a disc to the other. However, upon the switching of the heads, the direction of rotation of the disc has to be changed. In addition, the players are incapable of seamless play when switching from one side to the other.
As far as is presently known, the only device that has two (or more) heads and reads both sides of a disc while the disc is rotated in a single direction is a magnetic hard drive. However, this type of disc has only one layer of information on each side. Moreover, the data on the disc is arranged in concentric circles rather than spiral tracks, and therefore the drive needs a reading mechanism that is much simpler and far less accurate then the reading mechanisms used in an optical disc player.